Many industries require complicated manufacturing processes that must be conducted in a remote, automatic manner made necessary by the harsh conditions of the process. The end result of the process may generally be known only with some degree of uncertainty and is usually determined by stopping the process and analyzing a sample. A decision is made, based on the sample, to continue, discontinue, or alter the process. Costs and productivity can be affected by the timeliness of and time required for the sampling and testing, as well as the accuracy of the analysis. The metals industry is indicative of such concerns, as evidenced by an increasing need for on-line analysis of molten metal. Such analytical needs generally require that a restricted access to be maintained to the process even with the harsh conditions, and generally involves a long sampling and analysis time compared to the time of the process. The need for on-line analysis has increased in the metals industry due to an increasing use of continuous processing. In addition, the need for higher quality metal alloys has increased, total process lines have shortened, and energy costs have increased.
The present practice of the metal industry is to extract a sample from the melt at the predicted end of the refining process. The sample is rapidly cooled and transported to a laboratory for analysis. The process metal remains at temperature and continues its chemical activity during the analysis time. After the testing of the sample is complete, the metal is poured if the correct elemental ratios exist; further refining takes place if the testing indicates.
The ferrous metals industry represents some of the harshest sampling conditions and the largest volume of the metal industry. Several attempts have been made to provide rapid, in-process, elemental analysis of molten steel. Such analyses were based on taking emission spectra from the metal surface after excitation by ultraviolet or plasma methods and are described in U.S.Pat. Nos. 3,645,638; 3,659,944; 3,669,546; and 3,672,774. The lack of success in applying these techniques may be attributed to problems with optical coupling and the maintenance of delicate spectroscopic systems, cleaning and positioning of the excitation volume, and differential vaporization in the excitation volume.
Efforts to avoid the above problems were made by extracting the liquid metal in particulate form, as set forth in U.S. Pat. Nos. 3,606,540; 3,602,595; and 4,578,022.
A critical problem with past efforts using atomized metal powders in continuous elemental analysis procedures of liquid metals has been metal buildup on the inside of the probe wall. Such metal buildup can completely clog the probe core in a matter of minutes. Once clogged, these earlier probes had to be discarded after as few as one analysis procedure. To compensate for metal buildup on the internal probe walls of previous designs, extraordinary supplementary gas flow procedures as set forth in U.S. Pat. No. 3,606,540 were taken by others with minimal success.